Qt中事件分发源代码剖析(一共8个步骤,顺序非常清楚:全局的事件过滤器,再传递给目标对象的事件过滤器,最终传递给目标对象)

时间:2022-02-10 05:02:12

Qt中事件分发源代码剖析

Qt中事件传递顺序:

在一个应该程序中,会进入一个事件循环,接受系统产生的事件,并且进行分发,这些都是在exec中进行的。
下面举例说明:

1)首先看看下面一段示例代码:

  1. int main(int argc, char *argv[])
  2. {
  3. QApplication a(argc, argv);
  4. MouseEvent w;
  5. w.show();
  6. return a.exec();
  7. }

2)a.exec进入事件循环,调用的是QApplication::exec();

  1. int QApplication::exec()
  2. {
  3. return <span style="color:#ff6666;">QGuiApplication::exec();</span>
  4. }

3)QApplication::exec()调用的是QGuiApplication::exec();

  1. int QGuiApplication::exec()
  2. {
  3. #ifndef QT_NO_ACCESSIBILITY
  4. QAccessible::setRootObject(qApp);
  5. #endif
  6. return QCoreApplication::exec();
  7. }

4)QGuiApplication::exec()调用的是QCoreApplication::exec();

  1. int QCoreApplication::exec()
  2. {
  3. if (!QCoreApplicationPrivate::checkInstance("exec"))
  4. return -1;
  5. QThreadData *threadData = self->d_func()->threadData;
  6. if (threadData != QThreadData::current()) {
  7. qWarning("%s::exec: Must be called from the main thread", self->metaObject()->className());
  8. return -1;
  9. }
  10. if (!threadData->eventLoops.isEmpty()) {
  11. qWarning("QCoreApplication::exec: The event loop is already running");
  12. return -1;
  13. }
  14. threadData->quitNow = false;
  15. QEventLoop eventLoop;
  16. self->d_func()->in_exec = true;
  17. self->d_func()->aboutToQuitEmitted = false;
  18. int returnCode = eventLoop.exec();
  19. threadData->quitNow = false;
  20. if (self) {
  21. self->d_func()->in_exec = false;
  22. if (!self->d_func()->aboutToQuitEmitted)
  23. emit self->aboutToQuit(QPrivateSignal());
  24. self->d_func()->aboutToQuitEmitted = true;
  25. sendPostedEvents(0, QEvent::DeferredDelete);
  26. }
  27. return returnCode;
  28. }

5)QCoreApplication::exec()调用eventLoop.exec()进行事件循环;

  1. int QEventLoop::exec(ProcessEventsFlags flags)
  2. {
  3. Q_D(QEventLoop);
  4. //we need to protect from race condition with QThread::exit
  5. QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
  6. if (d->threadData->quitNow)
  7. return -1;
  8. if (d->inExec) {
  9. qWarning("QEventLoop::exec: instance %p has already called exec()", this);
  10. return -1;
  11. }
  12. struct LoopReference {
  13. QEventLoopPrivate *d;
  14. QMutexLocker &locker;
  15. bool exceptionCaught;
  16. LoopReference(QEventLoopPrivate *d, QMutexLocker &locker) : d(d), locker(locker), exceptionCaught(true)
  17. {
  18. d->inExec = true;
  19. d->exit = false;
  20. ++d->threadData->loopLevel;
  21. d->threadData->eventLoops.push(d->q_func());
  22. locker.unlock();
  23. }
  24. ~LoopReference()
  25. {
  26. if (exceptionCaught) {
  27. qWarning("Qt has caught an exception thrown from an event handler. Throwing\n"
  28. "exceptions from an event handler is not supported in Qt. You must\n"
  29. "reimplement QApplication::notify() and catch all exceptions there.\n");
  30. }
  31. locker.relock();
  32. QEventLoop *eventLoop = d->threadData->eventLoops.pop();
  33. Q_ASSERT_X(eventLoop == d->q_func(), "QEventLoop::exec()", "internal error");
  34. Q_UNUSED(eventLoop); // --release warning
  35. d->inExec = false;
  36. --d->threadData->loopLevel;
  37. }
  38. };
  39. LoopReference ref(d, locker);
  40. // remove posted quit events when entering a new event loop
  41. QCoreApplication *app = QCoreApplication::instance();
  42. if (app && app->thread() == thread())
  43. QCoreApplication::removePostedEvents(app, QEvent::Quit);
  44. while (!d->exit)
  45. processEvents(flags | WaitForMoreEvents | EventLoopExec);
  46. ref.exceptionCaught = false;
  47. return d->returnCode;
  48. }

6)eventLoop.exec()调用QCoreApplication的processEvents进行事件分发;

7)调用notify进行分发

QCoreApplication::sendEvent、QCoreApplication::postEvent和QCoreApplication::sendPostedEvents都调用notify进行事件分发;

  1. bool QCoreApplication::notify(QObject *receiver, QEvent *event)
  2. {
  3. Q_D(QCoreApplication);
  4. // no events are delivered after ~QCoreApplication() has started
  5. if (QCoreApplicationPrivate::is_app_closing)
  6. return true;
  7. if (receiver == 0) {                        // serious error
  8. qWarning("QCoreApplication::notify: Unexpected null receiver");
  9. return true;
  10. }
  11. #ifndef QT_NO_DEBUG
  12. d->checkReceiverThread(receiver);
  13. #endif
  14. return receiver->isWidgetType() ? false :<span style="color:#ff6666;"> d->notify_helper</span>(receiver, event);
  15. }

8)notify调用notify_helper进行事件分发;

  1. bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
  2. {
  3. // send to all application event filters
  4. if (sendThroughApplicationEventFilters(receiver, event))
  5. return true;
  6. // send to all receiver event filters
  7. if (sendThroughObjectEventFilters(receiver, event))
  8. return true;
  9. // deliver the event
  10. return receiver->event(event);
  11. }

9)从上面第8步的代码可以看出事件传递

传递的顺序是:首先传递给全局的事件过滤器,再传递给目标对象的事件过滤器,最终传递给目标对象。

http://blog.csdn.net/chenlong12580/article/details/25009095